Variable resistance device



Nov. 19, 1963 E. W. DIAL VARIABLE RESISTANCE DEVICE Filed June 15, 1962INVENTOR jdmrd l fl'dl BY WW ATTORNEYS United States Patent Ofi ice3,111,649 Patented Nov. 19, 1963 3,111, 40 VAREAEBLE REHSTANCE DEVICEEdward W. Dial, 815 Bnclrroe Ave, Hampton, Va. Filed lune 15, 1962, Ser.No. 202,840 3 Claims. (Cl. 338-160) The present invention relates ingeneral to variable resistance devices such as potentiometers,rheostats, volume controls and the like, and more particularly tovariable resistance devices of the potentiometer type wherein theresistance element is readily removable to facilitate repair orreplacement thereof.

l-leretofore, conventional variable resistance devices such, forexample, as a volume control potentiometer have been conventionallyconstructed in such a way that the resistance element cannot be removedfrom the encasing cover without substantial destruction of the device.Consequently, when such a potentiometer control element becomesdefective, it is usually necessary to unsolder the three conductorconnections to the terminals, physically remove the entire controldevice, install a new, complete control device and resolder the threeconnections to the terminals. This procedure not only entails a lengthywork process and its attendant possibilities for mechanical error, butalso involves considerable cost compared with repair procedures whereinonly a portion of the control device would be replaced. By far thegreatest majority of defects in potentiometer control devices requiringreplacement of a control are caused by a defect appearing in theresistance element.

An object of the present invention, therefore, is the provision of anovel variable resistance control device wherein the resistance elementis a separable component which can be readily removed and replaced witha minimum of time and efiort by unskilled personnel.

Another object of the present invention is the provision of a novelvariable resistance control device of simplified construction wherein aresistance bearing member of substantially rectangular platform or paneltype configuration is removably supported Within the cover in a mannerfacilitating simple removal of the resistance bearing panel andreplacement thereof.

Other objects, advantages, and capabilities of the present inventionwill become apparent from the following detail description, taken inconjunction with the accompanying drawings illustrating a preferredembodiment of the invention.

In the drawing:

FEGURE l is a perspective view of a variable resistance potentiometerconstructed in accordance with the present invention; I

FIGURE 2 is an exploded perspective view thereof with the componentsinverted relative to the position they assume in FIGURE 1;

FlGURE 3 is a vertical longitudinal section view taken along the line 33of FlGURE l; and

FIGURE 4 is a vertical transverse section view taken along the line 4 4of FIGURE 3.

Referring to the drawing, wherein like reference characters designatecorresponding parts throughout the several figures, an exemplary form ofa variable resistance potentiometer constructed in accordance with thepresent invention is indicated generally by the reference character ll)and comprises a casing 11 formed of a front wall member 12 and a cover13 secured thereto. The front wall member E2 is here shown as a rigid,rectangular plate having parallel lateral edges 14, 15 and upper andlower edges l6, 11.7 at least the lateral edges l4, l and one of theedges 16, 17 having rectangular notches l3 spaced along the same. Thecover 13 is a rectangular, box-like member having a rear Wall panel l9,and lateral side walls 20, 21 and top and bottom walls 22, 23 projectingforwardly from the rear panel 19 in perpendicular relation thereto. Ihelateral side walls 2d, 21 and the bottom Wall 23 in the embodimentherein illustrated having integral locking tabs 24 projecting from theforward edges thereof to seat in the notches l8 and be bent about thefront surface of the front wall member 12 to fix the cover 13 thereon.The cover 13 may be formed of sheet metal by cutting and bending a blankthereof or in any other desired manner.

An elongated operating shaft 25 extends through an aperture in the frontwall member 12 and is journaled for rotation therein by a suitablebearing or the like, such for example as an externally threaded bearingtube 26 through which the shaft 25 extends which is connected to orintegrally formed with the front wall member 12, the shaft 25 having anexternal end portion upon which a suitable operating knob may beprovided and an inner end portion 27 adapted to lie Within the chamber28 formed by the casing 11 having a key 29 on the end thereof. A wipermember 36 in the form of a circular disc, for example of insulatingmaterial, has a non-circular aperture 31 to fit over the shaft key 29and produce rotation of the wiper member 3%} with the shaft 25 and aperipheral contact ring 32 of conductive material having a contactprojection 32a at a selected point thereon projecting rearwardly of theplane of the ring 32. The ring 32 is continuously engaged by the centerterminal 34 of three terminal members 33, 34 and 35 electricallyinsulated from and mounted on the front wall member 12 adjacent the topedge 16 thereof and projecting externally of the casing 11. The wipermember 3% may also include a stop tab 35 which projects radially fromthe periphery thereof to engage a fixed stop stud or pin 37 on the frontwall member 12 projecting into the path of the stop tab 36 to limitrotation of the wiper.

The lateral side walls 2" 21 of the cover 13 are provided with inwardlyopening, parallel and transversely aligned groove or channel-shapedformations 38 in this example, formed by inwardly bent elongated beads39 or rib-forming indentations in the side walls 20, 21, definingrectilinear slideways within the casing 11 aligned with a laterallyelongated access opening 49 in the bottom wall 23 immediately adjacentthe rear wall panel 19 to receive a resistance insert 41. The resistanceinsert 41 is in the form of a rigid card or panel 42 of rectangularconfiguration formed for example of insulating material, having parallellateral edges 43 spaced apart substantially in conformity to the lateralinternal dimensions of the casing ll to be received in and guided by thechannelshaped formations 33. The panel 42 carries an electricalresistance element 44 of suitable resistance material thereon whichfollows a substantially arcuate path concentric with a point on thepanel to be aligned with the axis of the shaft 25 when the insert 41 isfully seated in the chamber 28 of the casing 11, and having portionswhich extend into electrical contact with the terminal members 33, 35 inbridging relation to the latter. In the embodiment illustrated, theresistance element 44 assumes the general configuration of the Greekletter omega with the feet adjoining the arc of the letter formingextensions to contact the terminal members 33, 35. A slot 45 opensthrough the top edge of the panel 42 to accommodate the end portion ofthe key 29 on the shaft 25 projecting rearwardly of the wiper memberduring sliding movement of the panel 42 relative to the casing, the slot45 having a circular enlargement at :me center of the arcuate portion ofthe resistance element when the resistance insert is fully inserted intothe casing.

The top wall 22 of the cover 13 forms a limit stop for the top edge ofthe insert 41, and the rear wall 1% of the cover 13 has oneormorebendable tabs 46 at the edge thereof boundingthe access opening 49 to be bent perpendicular to the plane of the rear wall 19 across theaccess opening 40 when the resistance insert 41 is seated in the casing11 and retain the insert 41 therein. An arcuate recess as indicated at4-7 may be provided in the lower edge portion of the rear cover wall 19between the tabs 46 to facilitate insertion and withdrawal of theresistance insert relative to the slideway therefor.

In the operation of the device, the wiper member 3i is assembled on thekey end of the shaft 25 in the usual manner, and the cover 13 isassembled on the front wall member 12 by fitting the same on the frontwall member with the locking tabs 24 seated in the rectangular notches13 and then bending the locking tabs 2d inwardly to lap the frontsurface of the front wali member. The resistance insert 41 is thenintroduced into the chamber 28 of the casing 11 by insertion through theaccess opening 49 and sliding the same upwardly along the slidewayprovided by the channel formations 38 in the side walls 19, 21 of thecover, as the top edge of the panel 42 abuts the top 22 of the cover.Thereafter, the tabs 46 are bent for- Wardiy across the access openingii) against the bottom edge of the panel 42 of the resistance insert 41.When the resistance insert is fully inserted into the casing, theextensions or feet of the resistance element 44- achieve a condition ofphysical and electrical contact with the terminal members 33, 35 inseries relation between these terminal members, and the contactprojection 32a of the contact ring 32 on the wiper member 3% is incontact with the arcuate portion of the resistance element 44. When itbecomes desirable to remove the resistance element for repair orreplacement, this can be readily accomplished by bending the tabs 46downwardly into substantially co-planar relation with the rear wall 19of the cover 13, and sliding the panel 42 on which the resistanceelement 4-4 is carried out of the slideway provided by the panelformations 38, and a new resistance insert may then be inserted and thetabs 46 bent forwardly again to support the same within the cover.

While but one preferred example of the present invention has beenparticularly shown and described, it is apparent that variousmodifications may be made therein within the spirit and scope of theinvention, and it is desired, therefore, that only such limitations beplaced on the invention as are imposed by the prior art and set forth inthe appended claims.

What is claimed is: i

l. A variable resistance potentiometer or the like comprising a casinghaving front and rear walls, lateral side walls and top and bottom wallsdefining an enclosed chamber therebetween, an operating shaft journaledin said front wall for rotation about its axis having an inner endportion disposed within said chamber, a wiper member supported on saidinner end portion of said shaft for rotation therewith having anelectrical contact portion projecting rearwardly therefrom eccentricallydisposed relative to the axis of said shaft, said casing side wallsincluding means defining a pair of laterally spaced parallel guidechannels providing a slideway along a plane perpendicular to the axis ofsaid shaft adjacent the inner end thereof, a resistance insert disposedwithin the chamber of said casing movable relative to said shaft andwiper member for sliding insertion and withdrawal from the casingindependently of said shaft and wiper member along a plane parallelingsaid front wall, said insert having a support panel of substantiallyrectangular configuration providing parallel spaced lateral edgesslidably supported in said guide channels and an electrical resistanceelement carried on said panel along an arcuate path concentric with theaxis of said shaft to be engaged by said contact projection on saidwiper member, said guide channels being located to dispose saidresistance element in sliding electrical and physical contact with saidWiper member when said panel occupies a selected position along saidplane, stop means providing an abutment for engaging an edge ofsaid'pa'nel are selected location along said plane to :locate saidresistance element in selected alignment with said Wiper member and theaxis of said shaft, said casing having an access opening thereinconforming substantially to the cross sectional configuration of saidresistance insert panel and aligned with said slideway for accommodatingpassage of said resistance insert therethrough, and said casingincluding bendable tab means extending from a portion of the casingbounding said access opening and bendable across portions of said accessopening to intercept withdrawal movement of said panel along saidslideway and hold said panel in position within said casing.

2. A potentiometer or the like comprising a casing including a rigidfront wall member of generally rectangular, planar configuration havingparallel lateral edges, a cover mounted on said front wall member ofgenerally box-like configuration having a rear wall disposed paraliel toand spaced rearwardly from said front wall member and integral top,bottom and side walls projecting forwardly from said rear wall andsecured at their front edges to said front wall member defining anenclosed chamber therebetween, an operating shaft journaled in saidfront wall member for rotation about an axis perpendicular to said frontwall member having an inner end portion lying within said chamber, awiper contact member coupled to the inner end portion of said shaft forrotation therewith, a generally rectangular removable resistance-bearingpanel forming a resistance insert in said chamber movable relative tosaid shaft and wiper contact member for insertion and withdrawalmovement from the cover independently of the shaft and wiper memberalong a plane paralleling said front wall member and intercepting theinner end portion of said shaft, said panel having parallel rectilinearlateral edges and a resistance element fixed on the surface of saidpanel facing said front wall extending along an arcuate pathsubstantially concentric with the axis of said shaft, means on saidlateral side walls of said cover defining rectilinear parallel guidechannels opening inwardly of the chamber to slidably receive saidlateral edges of said resistance insert panel in said plane and supoprtsaid panel in parallelism with said front wall member, said casingincluding stop means providing an abutment for engaging an edge of saidpanel transverse to said lateral edges to locate said panel in selectedalignment with the axis of said shaft, said panel having an openingtherein accommodating rotation of the inner end portion of said shafttherein when said panel occupies the selected alignment location andopening through the last-mentioned edge of said panel to permit passageof the shaft therethrough upon insertion and withdrawal movement of saidpanel along said plane, one of said top and bottom walls of said coverhaving an access opening therein aligned with the plane of saidresistance-bearing panel and conforming substantially to the crosssection thereof to accommodate insertion and removal of saidresistance-bearing panel therethrough, and bendable tab membersextending integrally from a portion of said cover bounding said accessopening across said access opening to close the same against withdrawalof said panel from said chamber.

3. The combination recited in claim 2 wherein said resistance elementhas an omega configuration providing an arcuate portion to be engaged bysaid wiper contact member and extension portions to be connected inelectrical communication with an external circuit.

References Cited in the file of this patent UNITED STATES PATENTS2,841,660 Tabet July 1, 1958 2,871,324 Budd Jan. 27, 1959 2,917,721Kelver et al. Dec. 15, 1959 3,015,000 Tabet Dec. 26, 1961 3,069,598Bailey et al. Dec. 18, 1962

1. A VARIABLE RESISTANCE POTENTIOMETER OR THE LIKE COMPRISING A CASINGHAVING FRONT AND REAR WALLS, LATERAL SIDE WALLS AND TOP AND BOTTOM WALLSDEFINING AN ENCLOSED CHAMBER THEREBETWEEN, AN OPERATING SHAFT JOURNALLEDIN SAID FRONT WALL FOR ROTATION ABOUT ITS AXIS HAVING AN INNER ENDPORTION DISPOSED WITHIN SAID CHAMBER, A WIPER MEMBER SUPPORTED ON SAIDINNER END PORTION OF SAID SHAFT FOR ROTATION THEREWITH HAVING ANELECTRICAL CONTACT PORTION PROJECTING REARWARDLY THEREFROM ECCENTRICALLYDISPOSED RELATIVE TO THE AXIS OF SAID SHAFT, SAID CASING SIDE WALLSINCLUDING MEANS DEFINING A PAIR OF LATERALLY SPACED PARALLEL GUIDECHANNELS PROVIDING A SLIDEWAY ALONG A PLANE PERPENDICULAR TO THE AXIS OFSAID SHAFT ADJACENT THE INNER END THEREOF, A RESISTANCE INSERT DISPOSEDWITHIN THE CHAMBER OF SAID CASING MOVABLE RELATIVE TO SAID SHAFT ANDWIPER MEMBER FOR SLIDING INSERTION AND WITHDRAWAL FROM THE CASINGINDEPENDENTLY OF SAID SHAFT AND WIPER MEMBER ALONG A PLANE PARALLELINGSAID FRONT WALL, SAID INSERT HAVING A SUPPORT PANEL OF SUBSTANTIALLYRECTANGULAR CONFIGURATION PROVIDING PARALLEL SPACED LATERAL EDGESSLIDABLY SUPPORTED IN SAID GUIDE CHANNELS AND AN ELECTRICAL RESISTANCEELEMENT CARRIED ON SAID PANEL ALONG AN ARCUATE PATH CONCENTRIC WITH THEAXIS OF SAID SHAFT TO BE ENGAGED BY SAID CONTACT PROJECTION ON SAIDWIPER MEMBER, SAID GUIDE CHANNELS BEING LOCATED TO DISPOSE SAIDRESISTANCE ELEMENT IN SLIDING ELECTRICAL AND PHYSICAL CONTACT WITH SAIDWIPER MEMBER WHEN SAID PANEL OCCUPIES A SELECTED POSITION ALONG SAIDPLANE, STOP MEANS PROVIDING AN ABUTMENT FOR ENGAGING AN EDGE OF SAIDPANEL AT A SELECTED LOCATION ALONG SAID PLANE TO LOCATE SAID RESISTANCEELEMENT IN SELECTED ALIGNMENT WITH SAID WIPER MEMBER AND THE AXIS OFSAID SHAFT, SAID CASING HAVING AN ACCESS OPENING THEREIN CONFORMINGSUBSTANTIALLY TO THE CROSS SECTIONAL CONFIGURATION OF SAID RESISTANCEINSERT PANEL AND ALIGNED WITH SAID SLIDEWAY FOR ACCOMMODATING PASSAGE OFSAID RESISTANCE INSERT THERETHROUGH, AND SAID CASING INCLUDING BENDABLETAB MEANS EXTENDING FROM A PORTION OF THE CASING BOUNDING SAID ACCESSOPENING AND BENDABLE ACROSS PORTIONS OF SAID ACCESS OPENING TO INTERCEPTWITHDRAWAL MOVEMENT OF SAID PANEL ALONG SAID SLIDEWAY AND HOLD SAIDPANEL IN POSITION WITHIN SAID CASING.